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Eosinophilic Asthma

What Are Eosinophils?

Eosinophils are a type of white blood cells whose natural role is to defend the body against parasites. But they also accumulate wherever allergic reactions take place, including allergic asthma. 

Blood is a mixture of liquid plasma and tiny blood cells, pumped round the body by the heart, through the arteries, capillaries and veins. The plasma contains nutrients and waste products, on their way to and from all parts of the body, and contains hormones and chemicals for the defense of the body, particularly those needed for blood clotting when we are injured and those which help us to destroy bacteria and viruses when we are infected.

Most of the cells are red blood cells which carry oxygen from our lungs to all parts of the body. Others are white blood cells which defend us against invasion by bacteria, viruses and other particles which get into our bodies. Eosinophils can amount to nearly 3 percent of the white blood cells in the body.

There are different kinds of white blood cells, each with its own role. When the body recognizes invasion by foreign bacteria, viruses or substances, white blood cells move from the blood to the place where the invasion occurred, and play their role in destroying or expelling the invader or substance. At the same time our bone marrow starts to make far more of the white blood cells, so their numbers in our blood increases.

The kinds of white blood cell are:

  • Neutrophils, which can remove and kill bacteria and particles of foreign material.

  • Lymphocytes, are the cells help tell our body the difference between substances which do or don’t belong there.

  • Monocytes, help break up foreign particles and substances for the lymphocytes, which can recognition of the small fragments.

  • Eosinophils, gather wherever there is a parasite infection or an allergic reaction such as allergic asthma, and then release chemicals. The chemicals are very efficient at fighting parasites, but they can also harm the body if released in the wrong place. So the lining of the lungs becomes damaged in asthma.

  • Basophils, (as well as mast cells) release histamine when an allergic reaction happens, but also other chemicals which are similar to histamine in effect.

  • Blood platelets, aid in clotting of the blood and protect us from bleeding dangerously from small injuries. 

What Role Do Eosinophils Play in Asthma?

Over the years, researchers have discovered that eosinophils play a pivotal role in immune development and asthma. Asthma and allergic disease occur when the immune system improperly responds to harmless environmental substances such as pollen or mold. Common allergic reactions include eczema, hives, hay fever, asthma, food allergies, and reactions to the venom of stinging insects such as wasps and bees.

Studies examining patients with mild asthma have shown that airway inflammation due to eosinophils is a typical characteristic, and, in fact, eosinophilic airway inflammation appears to be closely related to the risk of severe asthma exacerbations.

Advances in Eosinophilic Asthma Research and Care

Researchers are always looking for novel approaches to asthma care and one approach is to develop therapies that help reduce eosinophils in asthma patients. Clinical trials are currently underway to assess the effectiveness and safety of new treatments that affect eosinophils in patients with poorly controlled asthma. Results are not complete, but progress is encouraging since this new therapy has helped to significantly reduce eosinophils, improve airway function, and provide greater asthma control to patients in the trials.

© Asthma and Allergy Foundation of America
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